In electrical systems for controlling airplanes, it is necessary to provide the flight control station with means for selectively operating load switching devices located in various remote portions of the plane. The load switching device may actuate power lights, landing gear controls, flight control surfaces, and the like. Frequently, the loads require relatively large amounts of power. Ordinarily, a radial or local power wires of relatively heavy gauge supply the power buses which are located at strategic points throughout the aircraft.
It is necessary to locate control switches for the various loads at the flight station and the load switching devices near the locations of power utilization. The load switches must be capable of withstanding overload currents due to faults and short circuits momentarily before they are able to break the load circuits in response to overload sensing elements. Formerly, load circuit switches have been controlled through the use of operating coils energized directly from the control switches. The control wire thus had to be extended all the way from the control switch to the locations of the loads and was subject to exposure of high fault currents. This not only called for control switches capable of handling heavy currents, but it also required a relatively large gauge wire be extended all the way from the control switches at the flight station to the load circuit switch at each load location. An airplane usually has load switching devices, generally numbering in the order of many hundreds. Also, the load switching devices are frequently a substantial distance from the flight station. As a result, excessive wire weight and insulation was required to reduce the danger of smoke and fire hazards. In addition, circuit breakers which are especially crude electro-thermal or electro-magnetic devices were needed to protect the wiring.
It is accordingly an object of the present invention to provide a novel method and control system which avoids a need for extending relatively large gauge wire between each of the control switches energized from the voltage supply bus at a central control station and each of the remote locations of the load switching devices.
It is a further object of the present invention to provide a novel current limiting means, such as current limiting warning lights (CLWL's), at the control station to permit low power signals to be passed through the CLWL's and the control switches to supply control signals to solid state circuitry in the controllers or load switching devices located at strategic areas of power utilization.
It is also an object of the present invention to provide a novel system employing solid state circuitry in remote control circuit breakers (RCCB's) or controllers both to provide ultimate control of the circuit making and breaking the power circuits in response to control switch commands and in response to fault conditions in the control or power wiring. The CLWL's in response to such fault conditions will light to indicate fault conditions and will simultaneously limit the fault current in the control circuits and in the power circuits where solid state controllers are utilized.
A further object of the present invention is to provide a system for controlling the operation of load switching devices in either d.c. or a.c. load circuits. In the case of a.c. loads, it is an additional object of the present invention to use reactance elements, such as a.c. capacitors, in the load circuit to act as current limiting devices.
Still another object of the present invention is to provide a novel system utilizing CLWL's in the control circuit to provide fault indications in the miniature wire gauge control lines, and to provide by means of a clamp or ground on the control line an indication of faults in the power circuits.
It is still yet another object of the present invention to provide a novel system in which a single line of miniature gauge wire, e.g. 30 gauge or less, can be utilized for trip reset, status, and on-off control while minimizing smoke and fire hazards.
These and many other objects and advantages will be apparent from the claims and from the following detailed description when read in conjunction with the appended drawings.